1. Technical Field
The present invention relates to a colorimetry apparatus.
2. Related Art
A colorimetry apparatus that measures and evaluates the color of an object in an objective, precise manner is widely used. Alight irradiation method used in the color measurement is defined in JIS 28722. In one of the light irradiation methods defined in JIS 28722, a specimen is irradiated with light ray fluxes inclined to a normal to the surface of the specimen by 45±2°, and light ray fluxes reflected at angles smaller than or equal to 10° with respect to the normal to the surface of the specimen are received and measured. Irradiation light ray fluxes and reception light ray fluxes are limited to those inclined to the central line by 8° or smaller. The measurement method described above complies with the method for measuring the color of an object defined in Publication CIE NO. 15: 2004 COLORIMETRY, THIRD EDITION.
JP-A-8-29258 discloses a colorimetry apparatus using the light irradiation method described above. In the colorimetry apparatus disclosed in JP-A-8-29258, light emitted from a light source is collected by a collector lens and the collected light is allowed to pass through a diaphragm. The configuration allows a virtual image of the light source to be nearly a point light source. The light having passed through the diaphragm is then parallelized by a collimator lens. A surface under measurement is irradiated with the parallelized light in an oblique direction inclined to a surface under measurement by 45°. Divergent light reflected off the surface under measurement is collected by using a collector lens and an integrating sphere, and a spectrometer is irradiated with the collected light. An optical sensor is irradiated with the light having passed through the spectrometer. The optical sensor converts the intensity of the light into an electric signal and outputs the electric signal.
In the colorimetry apparatus disclosed in JP-A-8-29258, the optical axis of the collimator lens intersects a normal to the surface under measurement at an angle of 45°. As a result, the optical path length from the collimator lens to the surface under measurement varies depending on location in the parallelized light. The parallelized light having exited out of the collimator lens is not exactly parallelized but contains divergent light. The surface under measurement is therefore so illuminated that the illuminance varies from location to location on the surface under measurement. That is, the illuminance at a location where the optical path length from the collimator lens to the surface under measurement is longer is lower than the illuminance at a location where the optical path length is shorter. When the colorimetry apparatus performs colorimetry at a plurality of locations on the surface under measurement instead of a single location thereon, the non-uniform illuminance over the surface under measurement causes a decrease in measurement precision. In view of the fact described above, it has been desired to provide a colorimetry apparatus that irradiates a surface under measurement with light that provides a uniform illuminance distribution for colorimetry.